The Abad composite (SE Spain)

29 Pages·2001·0.92 MB·English

Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169
www.elsevier.nl/locate/palaeo
The Abad composite (SE Spain): a Messinian reference section for
the Mediterranean and the APTS
F.J. Sierroa,*, F.J. Hilgenb, W. Krijgsmanc, J.A. Floresa
aDepartmentofGeology,UniversityofSalamanca,37008,Salamanca,Spain
bDepartmentofGeology,FacultyofEarthSciences,UtrechtUniversity,Utrecht,TheNetherlands
cPaleomagneticLaboratory“FortHoofddijk”,UtrechtUniversity,Utrecht,TheNetherlands
Received7July1999;acceptedforpublication28August2000
Abstract
Ahigh-resolutionintegratedstratigraphyispresentedfortheAbadmarlsoftheSorbasandNijarbasinsinSESpain(pre-
evaporitic Messinian of the Western Mediterranean). Detailed cyclostratigraphic and biostratigraphic analyses of partially
overlappingsubsectionswereneededtoovercomestratigraphicproblemsinparticularencounteredatthecomplextransition
fromtheLowertotheUpperAbad.TheresultingAbadcompositesectioncontainsacontinuousstratigraphicrecordfromthe
Tortonian/Messinian boundary up to the transition to the Messinian evaporites of the Yesares Member. All together, 18
calcareous plankton events were recognized which were shown to be synchronous throughout the Mediterranean by means
of detailed (bed-to-bed) cyclostratigraphic correlations. The magnetostratigraphy allowed the identification of the four
magneticreversalsofchronC3AnintheUpperAbad.DetailsinthesedimentarycyclepatternsallowedtheAbadcomposite
tobeastronomicallycalibrated.Thiscalibrationtothe658NsummerinsolationcurveofsolutionLa90 yieldedastronomical
(1,1)
agesforallsedimentarycycles,calcareousplanktonbioevents,ashlayersandpaleomagneticreversals.Uptonow,theAbad
composite is theonly astronomicallywell-calibrated section thatprovided a reliablecyclostratigraphy, magnetostratigraphy
andcalcareousplanktonbiostratigraphy.Assuchitwillserveasareferencesectionbothforthepre-evaporiteMessinianinthe
MediterraneanaswellasfortheMessinianintervalintheAstronomicalPolarityTimeScale.q 2001ElsevierScienceB.V.All
rightsreserved.
Keywords:Biostratigraphy;Magnetostratigraphy;Milankovitch;Planktonicforaminifera;Mediterranean;Messinian
1. Introduction 1987;LangereisandHilgen,1991;Krijgsmanetal.,
1995, 1997). Detailed cycle pattern analysis have
During the last decade, high-resolution biostrati- allowed these sections to be tuned to astronomical
graphic,magnetostratigraphicandcyclostratigraphic target curves, resulting in astronomical time scales
studies of marine sections in the central and eastern forthePlio-Pleistocene(Hilgen1991a,b;Lourenset
Mediterranean have provided an excellent chronos- al.,1996)andthelateMiocene(Hilgenetal.,1995).
tratigraphicframeworkforthelateNeogene(Hilgen During the late Messinian, however, restricted
environmental conditions in the Mediterranean
caused a widespread deposition of evaporites,
* Corresponding author. Tel.: [phone]; fax: 1923-29-
preceeded by cyclic alternations of diatomites and
4514.
E-mailaddress:[email protected](F.J.Sierro). marls (e.g. Tripoli Formation of Sicily). These
0031-0182/01/$-seefrontmatterq2001ElsevierScienceB.V.Allrightsreserved.
PII: S0031-0182(00)00253-4
1
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Polopos
Cortijada
Arejos
Cortijada Almendral Gafares
Arejos section
HighwaytoAlmería
RoadtoNijar RamblaSaladilla RamblaGafares
Evaporites Abadmarls Calcarenites
Fig.1.Locationmapofthesectionsstudiedinthispaper:(above)SectionsoftheSorbasbasin;and(below)SectionsoftheNijarbasin.
F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 143
typesofsedimentsaredifferentfromthehemipelagic 2.General setting and stratigraphy
deposits of Pliocene and early Messinian age and
have until recently hindered the construction of an TheSorbasandNijarbasins(Fig.1)aresmallLate
astronomical time (polarity) scale for the late Neogene depressions that evolved in the Eastern
Messinian. Betics (SE Spain) in a structural corridor that was
Recently,ithasbeenshownthatthecyclicbedding subjected to compressional and extensional events
of the pre-evaporitic diatomites is related to astro- (Montenat and Ott d’Estevou, 1996). During the late
nomically controlled variations in regional climate Tortonian, a general uplift caused an important sedi-
as well (Hilgen et al., 1995; Sprovieri et al., 1996b; mentary discontinuity in both basins (Weijermars
Sierro et al., 1997, 1999; Krijgsman et al., 1999; et al., 1985; Martin and Braga, 1996), separating
Hilgen and Krijgsman, 1999; Vazquez et al., 2000). middle–upper Tortonian hemipelagic and turbiditic
Up to now, however, no section has provided a reli- sediments from the uppermost Tortonian–lower
able and continuous magnetostratigraphic record. Messinian pre-evaporitic deposits (Ott d’Estevou
TripolisectionsfromSicilyrevealasecondary(over- 1980; Van de Poel, 1991; Martin and Braga, 1996).
printed) normal magnetisation (Langereis and The pre-evaporitic sequence starts with calcarenitic
Dekkers,1992)orshowcontroversialresults(Gautier deposits of latest Tortonian age (Azagador member,
etal.,1994;McClellandetal.,1997).Sectionsinthe Vo¨lk 1964), overlying the middle–upper Tortonian
Northern Apennines (Italy) are subject to diagenetic sediments or, unconformably, the basement. These
overprintingandstrongtectonicdeformation(Krijgs- calcarenites of the Azagador member rapidly grade
manetal.,1997;NegriandVigliotti,1997),whilethe upward into marls, clays and diatomites of early
Metochia diatomite section on Gavdos (Greece) is Messinian age, generally classified in the literature
overprinted by a secondary reversed component as the Abad member (Vo¨lk and Rondeel, 1964). The
(unpublished data). baseoftheAbadmemberusuallyconsistsofayellow-
To date, the Abad marls of the Sorbas and Nijar ishsiltyunitofseveralmetersthickness,whichcanbe
basins in Southeast Spain are the only cyclically- regardedasatransitionalfaciesbetweentheAbadand
bedded stratigraphic unit in the Mediterranean that Azagador.
may provide a reliable magnetostratigraphy for the TheAbad marls, deposited inrelatively deep parts
pre-evaporiticMessinianfromtheTortonian–Messi- oftheSorbasandNijarbasins,usuallyinterfingerand
nian boundary to the base of the evaporites. Gautier gradelaterallyandverticallyintoplatformcarbonates
et al. (1994) reported the first magnetostratigraphic and reefs (Cantera member, Vo¨lk 1964) that grow
data from the Sorbas basin, correlating the Abad along the margins in shallower waters (Dronkert and
marlstochronsC3Bn,C3Ar,C3AnandC3r(Gilbert Pagnier, 1977; Ott d’Estevou, 1980; Dabrio et al.,
Chron) and the evaporites (Yesares member) to the 1985; Martin and Braga, 1990, 1994, 1996; Braga
lower part of chron C3r. The cyclostratigraphic and Martin, 1996). Several studies have identified an
potentialoftheAbadmemberwasfurtherevaluated upwardchange,bothinsedimentaryfaciesandmicro-
by Sierro et al. (1997, 1999), showing that the sedi- paleontologiccontent,allowingtheAbadmarlstobe
mentarycyclicitywascontrolledbytheastronomical dividedintotwodistinctunits.(Geerlings1977;Dron-
precession cycle. kertandPagnier,1977;Civisetal.,1979;Ottd’Este-
The Abad member is therefore suitable for estab- vou, 1980; Van de Poel, 1991; Sierro et al., 1997,
lishinganastronomicalpolaritytimescale(APTS)for 1999;Vazquezetal.,2000).TheLowerAbadischar-
thecrucialperiodoftimethatheraldstheonsetofthe acterisedbyanalternationofinduratedhomogeneous
Messiniansalinitycrisis(seeKrijgsmanetal.,1999). whitishmarlsandsofterhomogeneousgreymarlsrich
This study mainly focuses on the elaboration of an in planktonic foraminifera. Grey-brownish laminated
integrated stratigraphy for the Abad Member, which sediments,hereafterreferredtoassapropels,areonly
will be used to establish a standard chronostrati- interbeddedinitsuppermostpart.TheUpperAbadis
graphicframeworkbothforthepre-evaporiticMessi- recognised in the field by its brownish colour and is
nian of the Mediteranean as well as for the late characterised by the intercalation of sapropels and
Messinianinterval ofthe APTS. indurated diatom-rich (diatomites) layers containing
144 F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169
more benthic foraminifera and plant remains. These middle part of the Upper Abad (Civis et al., 1979;
diatomites are faintly laminated at the base and Gonzales Donoso and Serrano, 1977; Geerlings,
strongly laminated (paper shales) towards the top. 1977;VandePoel,1991;Sierroetal.,1993;Gautier,
AnothercharacteristicoftheUpperAbadistheinter- etal.,1994).Thislattereventhasbeenwidelyrecog-
calationofverythinlaminaeofdistalsandyturbidites nisedthroughouttheMediterraneanbelowtheLower
within the sapropels, indicating increasing grain-size Evaporites,orthelaterallyequivalentCalcarediBase
interrestrialinput into the basins. (Zachariasse,1975;Colalongo,etal.,1979;Sprovieri,
During deposition of the Lower Abad, sedimenta- et al., 1996a,b). Furthermore, a general impoverish-
tionwascontinuousinmostareas.However,thelimit ment of the microfauna is observed immediately
betweentheLowerandUpperAbadismarkedeither preceding the evaporite deposition in the Mediterra-
byahiatusnearthemarginsorbysedimentinstability, nean (D’Onofrioet al., 1975).
as evidenced by several slumps (multiple-slump BoththeAbadmarlsinthecentralpartofthebasins
event) that transported Lower Abad relicts into andtheCanteramemberalongthemarginsareover-
UpperAbadmarls,depositedinthebasindepocenters. lainbymassivegypsumdepositswithlaminatedpeli-
The sedimentary instability was probably due to ticintercalations(Yesaresmember,Ruegg1964).The
tectonic uplift of the basin margins, creating steep Yesares member is commonly correlated with the
slopes that favoured sediment sliding into the deeper Lower Evaporites of the Central Mediterranean
regions. In the Sorbas basin, the tectonic activity (Mu¨llerandHsu¨,1987;Gautieretal.,1994;Clauzon
started during deposition of the upper part of the et al., 1996; Krijgsman et al., 1999), although some
Lower Abad (i.e. from cycle LA17 upwards) but authors have proposed a correlation with the Upper
was intensified at the onset of the formation of the Evaporites (Martin and Braga, 1994; Riding et al.,
Upper Abad. This tectonic event might be the same 1998, 1999).
asthe onethatcauseda regional unconformityalong
the basinal margins (Martin and Braga, 1994, 1996).
3. Sections studied
Messinian reefs of the Cantera member lie uncon-
formably above the Azagador and lowermost Abad.
Four sections (Molatas, Molinos, Gypsum quarry,
This unconformity was caused by erosion of all, or
Perales)intheSorbasBasin(Fig.1)andtwo(Almen-
part,ofthe Lower Abadalongthebasinmarginsand
dral,Gafares)intheNijarBasinwerestudiedtoobtain
mighthaveextendedtowardsthebasincentres,where
a continuous and complete record of the Abad
sedimentation was only interrupted by the sliding of
member, i.e. from the top of the calcarenites to the
several repetitive slumps. A second slump is located
base ofthe evaporites.
in all Upper Abad sections of the Sorbas basin. This
slumpcouldberelatedtotheunconformitythatsepa-
3.1. Sorbas basin
ratesthebiohermunitfromthefringingreefunit,two
marginal facies of the Upper Abad according to TheMolatassectionisacompositeof2subsections
Martin and Braga (1994, 1996). exposed along the old road from Sorbas to Nijar,
TheAbadmarlshavealwaysbeenconsideredtobe between Km 6 and 7 on the southern side of the Rio
ofearlyMessinianageandbelongtotheGloborotalia Aguas (Fig. 1). Molatas A is a short subsection that
mediterraneaandGlobigerinamultilobasubzonesof covers the yellowish silts overlying the calcarenite
D’Onofrioetal.(1975)(Iaccarinoetal.,1975;Civiset and the lowermost part of the Abad marls. Molatas
al., 1979; Gonzales Donoso and Serrano, 1977; Van B extends from the top of the yellowish silts and
dePoel,1991;Sierroetal.,1993).ThebaseoftheG. comprises mostofthe Lower Abad (Fig. 4).
mediterranea subzone was recognized near the base TheMolinossectionislocatedonthenorthernside
of the Abad marls (Gonzales Donoso and Serrano, of the Rio Aguas, 500m north of Molatas, and also
1977; Sierro et al., 1993, 1996). The limit between comprises two subsections. The base of Molinos A
the G. mediterranea and G. multiloba subzones was starts immediately above the multiple-slump event
approximately correlated with the coiling change in that marks the limit between the Lower and Upper
Neogloboquadrina acostaensis that occurred in the Abad (Figs. 2 and 4). Several white indurated layers
F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 145
1a Molinos B 1b Molinos A
2
3
A
U
o 2 2
t A
9 U
2 8 o
UA A2 A 4 t
U U
o
t 4
23 U A
UA 3 to
TopofSlump A
U
1c
Gypsum Gypsum
Slumps
Abad
Calcarenite
2
Perales A Perales C Perales B
Gypsum
UA23toUA34
LA13 LA15 LA17 UA4toUA22 Slump UA1 SapropelLA20 Slump LA18 to LA21
UA3toUA4
LA9 UA2 LA20 Slump LA17
Fig.2.PhotographsoftheMolinossubsections.1cPanoramicwiewshowingthecalcarenites(Azagadormember)atthebase,theAbadmarlsin
themiddleandtheGypsumunit(Yesaresmember)ontop.ThelocationofsubsectionsAandBisalsoshown.1aand1b:Picturesshowingthe
samplingtrajectoriesofsubsectionsAandBandthecyclesidentifiedineverysubsection.2:Photographshowingthesamplingtrajectoriesof
thePeralessubsectionsA,BandC.Thegypsumunitisontopofthehill.
146 F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169
Fig.3.Top:PhotographshowingthesamplingtrajectoriesoftheGafaressectionindicatingthedifferentintervalsbythecyclenumbers.
Bottom.DetailedpictureoftheLowerAbadinGafaresshowingthecharacteristicalternationofinduratedlayersandhomogeneousmarls.
CyclesLA11–LA15weresampledinthisgully.
are present in the lower part while thin, well-lami- slumpunitinthetoppartofMolinosAasthestarting
nated diatomites (paper shales) occur towards the point of Molinos B. In the latter section, a few very
top.Becausetheupperpartofthissectionwascapped prominent paper shales are clearly visible in the
byPlio-Pleistoceneconglomerates,wesampledMoli- weathered outcrop. Unfortunately, the uppermost
nosB(nextgullytothenorthwest,Fig.2)tocomplete levels and the transition to the Gypsum are not well
theuppermostpartoftheUpperAbad.Itwaspossible exposed.
tocorrelatebothsubsectionsbylateraltracingofsome TheGypsumquarrysectionconsistsoftwosubsec-
markerbeds.Wechosethedistinct,6.5mthick,upper tions lying on both sides of a tributary of the Rio
F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 147
Aguas, immediately to the east and southeast of the showing the characteristic indurated layers (see
maingypsumquarry(Fig.1).Gypsumquarrysection Fig. 3). This is the only section in which sedimenta-
A shows yellowish silts at the base, immediately tion was continuous in the Lower to Upper Abad
abovethetopofthecalcarenites(Azagadormember). transition, showing no evidence for slumping or
These silts gradually pass upward into grey marls, hiatuses. The section has been extended to the
recordingmostoftheLowerAbad(Fig.4).Insection base of the evaporites but the uppermost part is not
B, the limit between the lower and Upper Abad is well exposed and shows clear indications of tectonic
recorded by a sharp change in colour and lithology. deformation.
TheUpperAbadisalmostcompletebutcyclebedding The Almendral section is found approximately
is not clearly visible in the exposures because of 5km west of Gafares. It covers most of the Lower
surface weathering. However, several prominent Abad and the lower part of the Upper Abad (Fig. 4).
paper shales can be clearly distinguished in the ThelimitbetweentheLowerandUpperAbadisvery
upper part of the gullies below the gypsum. Two sharp, suggesting the existence of a hiatus. Both the
slump intervals were recognized: the first, of 1.5m, indurated layers as well as some thick sandstone
is characterised by small-scale deformations in the layersinthelowerpartofthesectionareclearlyvisi-
firstsapropeloftheUpperAbad;thesecondisclearly ble.SapropelsarealreadypresentintheLowerAbad
visible in the upper part. Above the upper slump, buttheyaregreyincolour.TheUpperAbadcyclicity
prominent paper shales are slightly folded indicating isevidentbuttheidentificationofseveralshearplanes
tectonic deformation. Part of the succession, which parallel to the bedding prevented us from being
contains two of the prominent paper shales, has certain about the cycle correlations. The Almendral
even been tectonically doubled. This repetition was sectionisoverlainbyPlio-Pleistoceneconglomerates.
confirmed by means of a detailed comparison with Some paper shales are visible near the top. Many
the other Abad sections which provided an excellent small faults are present but individual layers can
high-resolution control onthe cyclostratigraphy. readily betraced.
The Perales section is located on the northern side
of the Rio Aguas, approximately 2km north-east of
the village ofLosMolinos(Figs.1 and2).Perales A 4.Cyclostratigraphy and tephrastratigraphy
records part of the Lower Abad, while Perales B
reveals the transition between the Lower and Upper In the Lower Abad sedimentary cycles are defined
Abad, recording the multiple-slump event that by the cyclic occurrence of indurated layers interca-
includes part of the Lower Abad in this section lated within the homogeneous marls (see Fig. 4).
(Fig. 4). Two very thick and prominent sapropels These indurated layers are between 20 and 60cm
that mark the base of the Upper Abad can easily be thick and are usually characterised by abundant
tracedlaterallyalongthedifferentgullies(seeFig.2), Opal Ct (Sierro et al., 1997, 1999; Vazquez et al.,
indicatingthatsedimentationcontinuedinthispartof 2000). Because there are no sapropels in most of the
the basin after each slump event. Perales C extends Lower Abad we used the bottom of the indurated
fromtopofthemultiple-slumpeventtothebaseofthe layers as the lower limit of the cycles. Based on
Evaporites. Although some small-scale deformation these criteria, we defined cycles LA1–LA21. In the
was observed near the base of Perales C, sedimenta- UpperAbad,asapropeliticlayerappearsinthemiddle
tion was continuous. partofthehomogeneousmarlsbetweentwoconsecu-
tive indurated layers. We used the base of the sapro-
pels to define the limits of the cycles to maintain the
3.2. Nijar basin
samecriteriausedinotherMediterraneansapropelitic
The Gafares section is located on the northern sections. Cycles UA1–UA34 were recognized in the
margin of the Nijar basin near the village with the UpperAbad.Becauseofthischangeinthedenomina-
same name, on the right side of the road from this tionofthecyclesbetweentheLowerandUpperAbad,
village to El Saltador bajo (Fig. 1). In the Gafares cycleLA21andcycleUA1arepartiallythesame(see
section,mostoftheLowerAbadisperfectlyexposed, Fig.4).
148 F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169
F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 149
In the lowermost part of the Abad, immediately usuallythin.Thecyclicsedimentationendswithcycle
above the yellow silts, cyclicity is not evident, UA34, which is overlain by a transitional interval to
althoughsomesections(e.g.MolatasAandGypsum the Gypsum, characterised by the presence of clays
Quarry A) show indications of slightly more indu- and limestones. The transition to the Gypsum is
rated layers alternating with homogeneous marls always poorly exposed and therefore cyclicity is not
(Fig. 4). Cyclicity starts to be clearly discernible easily recognisable inthe field.
with the occurrence of a first prominent indurated Three biotite-rich levels were identified in our
layer that lies several metres above the base of the sections. The lowermost ash layer was found inme-
marls. Because this is the first well distinguishable diately belowthe indurated layer ofcycle LA1. The
lithological cycle in all sections, we termed it as middle ash layer was found within LA17. On top of
Abad Cycle 1 (LA1) (Fig. 5a). It is followed by sapropelUA1twothinashlayersoflessthan0.5cm
cycles LA2, 3 and 4, which are usually thinner than thicknessareseparatedbya2cmthickmarllayerin
normal.IntheSorbasbasin,induratedlayersofLA9 section Perales, whereas up to 6 or 7 very thin
andLA10arealwaysprominent,incontrasttoindu- biotite-containing ash layers are found in the corre-
rated layer 11, which is usually thin. In the Nijar lative cycle in the Gafares section. These character-
basin, this pattern is less clear. Cycle LA12 is the istic layers, together with the high-resolution
thickest cycle, both in the Sorbas and Nijar basins. biostratigraphy, were very useful for the correlation
The homogeneous marls of cycle LA15 is always of the sections in the complicated multiple-slump
extremely thin and the homogeneous marls of cycle interval.
LA16isalsolessthickthaninmostothercycles.The
characteristic pattern of cycle LA15 and LA16
5.Biostratigraphy
provides one of the most useful criteria for cyclos-
tratigraphic correlations in the Lower Abad (see
Biostratigraphy was mainly based on quantitative
Fig. 4). In the Nijar basin (Almendral and Gafares
and qualitative changes in the planktonic foraminif-
sections),thefirstsapropeloccursinthemiddlepart
eral assemblages (Figs. 5 and 6) although some
of the homogeneous marls of cycle LA17. In the
nannofossil results are presentedas well.
Perales section, which is probably located near the
depocenteroftheSorbasbasin,thefirstsapropelalso
5.1.Keeled globorotaliids
occursincycleLA17.Inmoremarginalsettings(i.e.
Molatas B), sapropels were not formed until cycle The groups of Globorotalia menardii (dex.) and
(UA1) (LA21). Globorotalia miotumida (sin.) that play a keyrole in
In the Upper Abad, cycles UA6 and UA7 have Mediterranean and Atlantic correlations were identi-
distinct sapropels, while the sapropels of cycles fiedinalloursections.SpecimensofG.menardiidex
UA5,UA9andUA11arepoorlydeveloped.Besides, wereonlyfoundinthelowermostsamplesoftheAbad
cycleUA4ismuchthickerthanaverage.Higherinthe marls, inmediately above the top of the transitional
succession, the very thin sapropel of LA13 and the yellowish silts (Figs. 4 and 5). The last occurrence
thicker-than-average homogeneous bed of UA17 are (LO) of this group is followed 50cm upward by the
characteristic. In the uppermost part, the sapropel of first regular occurrence (FRO) of the Globorotalia
UA31 is a good marker because it is very thick and miotumida group (Figs. 4 and 5). Both groups do
weaklylaminated.Incontrast,thesapropelofUA32is notcoexist in oursections.
Fig.4.Cyclostratigraphicandbiostratigraphiccorrelationsofallsectionsstudiedinthispaper.1.LOoftheofthegroupofGmenardiidex.2.
FrOoftheG.miotumidagroup.3.InfluxofthehighlyconicalformsoftheG.miotumidagroup.4.TopoftheparacmeofR.pseudoumbilicus.5.
LAOofthegroupofG.scitulasin.6.StrongreductionofthegroupofG.scituladex.7.BottomacmeofthegroupofG.scituladex.8.Top
acmegroupofG.scituladex.9.FAOofG.siphonifera.10.LastinfluxoftheG.miotumidagroup.11.LrOoftheG.miotumidagr.12.First
abundantinfluxofT.multiloba.13.LastabundantinfluxofsinistralNeogloboquadrinids.14.FirstabundantinfluxofdextralNeogloboqua-
drinids.15.ShortinfluxofthegroupofG.scituladex.16.InfluxsinistralNeogloboquadrinids.17.ShortinfluxofthegroupofG.scituladex.
18.Influx.sinistralNeogloboquadrinids.
150 F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169
Fig.5.Abundancevariationofsomeoftheplanktonicforaminiferausedtodefinethemainbioevents.(a)FromthebaseoftheAbadmarlsto
cycleA34.(b)FromcycleA34tothebaseoftheEvaporites.Magnetostratigraphyfromcycles1to20inferredfromKrijgsmanetal.1995and
fromcycles20to55basedonthispaper(seeFig.7.Thiscompositeisbasedonthefollowingsections:MolatasA,MolatasB,MolinosAand
MolinosB.LAG.menar.dex.(cid:136)LastoccurrenceofGloborotaliamenardiidextral.FrOG.miotum.Gr.(cid:136)Firstregularoccurrenceofthe
Globorotalia miotumida group. R. Pseudoumbilicus(cid:136)Reticulofenestra pseudoumbilicus, LAO group G. scitula sin.(cid:136)Last Abundance
OccurrenceofthegroupofGloborotaliascitulasinistral.Gr.G.scituladex.(cid:136)GroupofGloborotaliascituladextral.FAOG.obesa(cid:136)First
abundantoccurrenceofGlobigerinaobesa.Lastr.Occurrence(cid:136)Lastregularoccurrence.Percentageofthedifferenttaxainrelationtototal
planktonicforaminiferawiththeexceptionofthefirstcolumnin5bwhichshowsthepercentageofsinistralNeogloboquadrinidsinrelationto
totalNeogloboquadrinid.